add missing break like in older patch

--- a/squashfs-tools/unsquashfs.c
+++ b/squashfs-tools/unsquashfs.c
@@ -1481,6 +1481,7 @@
 			SQUASHFS_SWAP_SUPER_BLOCK_3(&sblk, &sBlk_3);
 			memcpy(&sBlk_3, &sblk, sizeof(squashfs_super_block_3));
 			swap = 1;
+			break;
 		} else  {
 			ERROR("Can't find a SQUASHFS superblock on %s\n",
 				source);